Creep Characterization of Phenolic Composites for Fastening and Sealing Design

Phenolic composites are replacing metals in a number of automotive engine and transmission components. Phenolics’ high elastic stiffness and excellent creep resistance enable the design of bolted engine components without requiring costly and heavy metal mounting boss inserts.

The creep performance of a phenolic composite has been characterized as a function of stress, time, temperature and degree of cure (T_g). Creep strain ε(t) is shown to be proportional to applied stress σ. The effect of time is characterized as “primary creep” (ε(t) = A + Bt^c), with C=0.25 providing a good fit across a broad range of conditions. The phenolic material's creep performance is shown to depend on temperature and T_g only through the reduced temperature variable (T_g - T).

Design equations are presented which describe the measured elastic and creep strain versus stress, time, temperature and T_g.